Some movies, while never quite attaining masterpiece status, nonetheless have a monumental WTF-factor. This is one such: a vampire horror thriller from freezing-cold Sweden, trebling up unwholesomely as a teen love-story and a bully-victim revenge fantasy. The director is Tomas Alfredson, and the screenplay is by John Ajvide Lindqvist, adapted from Lindqvist's own novel. The resulting grisly nightmare is much closer to Abel Ferrara than Stephenie Meyer, although there may be a tiny debt to JK Rowling in there somewhere. Let the Right One In is thoroughly macabre, maintaining a downbeat, realist lugubrious air, like a cop procedural - but there's no point waiting for Kenneth Branagh's careworn Wallander to come trudging through the snow to save the day. Oddly, with its oppressive suburban setting and teenage angst, it did look a little like Lukas Moodysson's 1998 debut, Fucking Åmål.

Kåre Hedebrant plays Oskar, a shy, unhappy 12-year-old boy who lives with his divorced mother in a Stockholm suburb. One snowy night, when he sees a taxi pull up outside his apartment building bringing new tenants for the vacant property next door - an older man and younger girl - he may be wondering if these new people will bring some excitement into his life. They do. The man, Håkan (Per Ragnar) is a serial killer whose modus operandi is to befriend young men, overcome them with a homemade anaesthesia kit and then cut their throats to collect the blood in an empty two-litre milk carton. This will be taken home for the girl Eli (Lina Leandersson), who turns out to be not his daughter but his eternal undead mistress, whose unending thirst has to be slaked at all costs.

Eli befriends Oskar when she sees him bitterly stabbing a tree, practising a longed-for fightback against the boys at school who are making his life a misery. Eli's anaemic beauty and eerie self-possession captivate Oskar; she wears only a thin dress in the snow and he asks her if she isn't cold. "I've forgotten how," is her calmly wondering response, as if she hasn't realised it before. As their relationship deepens, Eli advises Oskar to fight back against the bullies - "harder than you dare". The two fall passionately in love.

Alfredson shows how the burden of the undead is like the burden of childhood when the child realises how inadequate the parent is: Håkan is entirely incompetent as a serial murderer, and Eli must become a predator herself. When Håkan makes a mess of his final hit, and has to obliterate his own face with acid so as not be apprehended by the police, Eli's night-time visit to him in hospital - swooping up to the window in true Bram Stoker style - is a mind-boggling scene, bizarre and stomach-turning. The sequence of grotesque events is so outrageous that it is almost, but not quite, funny.

A strange, shabby chorus provides a counterweight to the grotesque horror, and later becomes a part of it. Gregarious and morose middle-aged drinkers collect in the bar close to Eli's apartment and she sizes them up as victims. Eli manages to bite the blowsy blonde Ginie (Ika Nord) in the street before being swatted away by a fellow boozer - too drunk to be fully horrified - and Ginie falls sick with what she thinks is a simple infection, before the nature of her transformation dawns on her: it is a moment that reminded me of Ferrara's The Addiction. Her new world of existential vampire agony leads to an attack by domestic cats and spontaneous combustion. Again, very satisfyingly bizarre scenes.

Alfredson and Lindqvist have perhaps sacrificed the value of narrative in favour of horror and fear, though they have one deliciously effective moment of old-fashioned suspense when Oskar finally strikes back against the bad kids during a school skating lesson, and two young girls appear to be horrified at the violence of which he is capable - but their dismay is then revealed to be caused by something entirely different, a revelation spring-loaded into the screenplay by an earlier event.

The film's title, as well as avowedly being a reference to Morrissey, alludes to the tradition that a vampire cannot enter your home if he or she has not been invited in. Alfredson and Lindqvist shape this trope into something else: an expression of love and commitment. Eli loves Oskar, but must be "invited in" to his life. When he refuses ritually to invite her over the threshold into his mother's flat, her emotional pain expresses itself horribly in bleeding from her eyes, ears and pores: a haemophilia of rejection.

She, after all, has invited Oskar into her flat, an empty, squalid mess. Yet she has one possession that she claims is equivalent in price to a nuclear power station - it is a Fabergé egg. Like so many of the movie's constituent elements, this is simply bizarre: part of a constellation of freakiness and fascination. Let the Right One In has invention and stamina, a rich arterial flow of fear.

Jason Solomons marks the centenary of the birth of James Bond producer Cubby Broccoli by talking to his daughter Barbara. Plus, an interview with the director of Swedish vampire flick Let The Right One, Tomas Alfredson